It should be known that this function also casts all of the values of the array to floats. If you pass an array of integers, they will come out as an array of floats.
$data = array(2,3,3,3,3,2,5);
var_dump($data);
$standardDeviation = stats_standard_deviation($data);
var_dump($data);
Prints:
array
0 => int 2
1 => int 3
2 => int 3
3 => int 3
4 => int 3
5 => int 2
6 => int 5
array
0 => float 2
1 => float 3
2 => float 3
3 => float 3
4 => float 3
5 => float 5
6 => float 2